Study Indicates Ants May Feel Self-Doubt

A pair of scientists from the University of Regensburg in Germany claim they've conducted a study that shows ants know when they don't know something, and that they react accordingly with doubt.

Typically, a colony of ants works together by leaving pheromone trails to help one another find food. But scientists Tomer Czaczkes and Jürgen Heinze found that when they created an unpredictable situation for test ants, they were less likely to leave such a path for their sisters to follow.

The study involved encouraging black garden ants to find food on a T-shaped maze. At first, the food was consistently placed in one arm of the maze. When the scientists switched the location of the food to the other arm, ants heading to the now-foodless location were less likely to leave a trail.

Once the ants had successfully found the food again, they left an even stronger trail of pheromones on their way back to the colony—presumably in the hopes that doing so would override the now-false information from before. But the most striking aspect of the study came when ants chose to check the newly-empty arm—this time, they didn't leave behind any pheromones at all.

"After finding the new food location once, they still usually think that the food is in the old location—they're just not sure," says Czaczkes.

This ability to recognize what is definite information and what is doubtful hints at a level of metacognition previously unseen in insects (except bees). Still, not everyone thinks that is what is happening.

"Ants might have other motives, such as exploring. And when exploring, they might not lay down as much pheromone," says Ken Cheng, from Macquarie University in Sydney, Australia. Joachim Zeil of the Australian National University posits that the behavior could be accounted for by thinking of it as a statistical anomaly.

The scientists behind the study maintain that they're on to something. "We don't have a smoking gun just yet for the definite proof of metacognition in ants, but we've got plans to find it," says Czaczkes.

Some insects’ mouth-to-mouth exchanges transmit tiny molecules of hormones and other important chemical information, according to scientists writing in the journal eLife.

The spit-swapping behavior is called trophallaxis. Many entomologists who witnessed the behavior in ants and other social insects believed the bugs were using it to efficiently share food. But some researchers noticed that carpenter ants were trophallax-ing in non-dining contexts, like when one ant would return to its family after being away. The scientists wondered if the ants’ kissing juice contained more than just calories.

They brought lots of ants into the lab to sample what the ants were sharing. At first, the researchers tried just waiting around until one ant initiated trophallaxis, but that mostly resulted in a lot of waiting and very little fluid. Eventually, they figured out that they could gently squeeze the ants’ bellies until the liquid came dribbling out of their mouths.

The researchers ran chemical and genetic tests on the fluid to determine its contents, and they found all kinds of interesting things. The liquid did indeed include particles of food and digestive enzymes, but it also contained several growth-related proteins and a juvenile hormone that can influence an insect’s development.

To find out how these compounds might affect a trophallaxis recipient, the researchers added the juvenile hormone to the meals they were feeding adult ants. The adults passed the hormone-charged liquid onto their larvae. The larvae loved it. Individuals who had taken in the hormone were twice as likely as others to survive to adulthood.

First author Adria LeBoeuf works at the Center for Integrative Genomics in Switzerland. She says the ants could very well be using trophallaxis to decide which larvae succeed. “When the ants feed their larvae, they aren’t just feeding them food, they are casting quantitative ballots for their colony, administering different amounts of growth-promoting components to influence the next generation,” she said in a statement.

Larvae chosen to receive the liquid are being nourished in more ways than one. In some ways, LeBoeuf says, it’s a lot like mammals’ milk. It also suggests that “…the oral exchange of fluids, such as saliva, in other animals might also serve previously unexpected roles." Yum.

In the Peruvian rainforest, a mutualistic relationship thrives between Inga tree saplings and native ants. The young trees need the ants as defense, so insects don't eat their leaves. The ants get "paid" for this defensive role using nectar provided by the tree.

In this beautiful Ultra-HD video from Deep Look, we see how this relationship works—and how it breaks down when clever Riodinid caterpillars come along!